An endotracheal tube (ETT), which provides an open airway to the patient's lungs, is inserted into the patient's trachea, in a process known as intubation. A balloon-like cuff near the distal end of the ETT, and in communication with a thin conduit embedded within the ETT wall, is inflated within the trachea and prevents leaks around the ETT.
After intubating a patient and setting the ventilation parameters, the physician inflates the cuff by a syringe and checks for leakage by means of an imprecise osculating stethoscope. The cuff is generally inflated to a pressure between 20 and 30 cm H2O, while ensuring that the Intra-Cuff Pressure (ICP) will not exceed 40 cm H2O to prevent damage to the tracheal tissue. An overinflated cuff during prolonged intubation is liable to damage the tracheal mucosa, including mucosal tracheal stenosis, ulceration, fistula, and granulomas. It is also important that the cuff is sufficiently inflated to adequately seal against the tracheal wall and to prevent aspiration of secretions and gastric influx which are liable to lead to ventilator-associated pneumonia (VAP).
A common prior art technique for measuring the ICP is by means of an analog indicator placed in fluid communication with the interior of the syringe barrel. However, the syringe barrel interior volume varies while the ICP is being regulated, and therefore the pressure reading is not accurate since the instantaneous volume of the barrel and of the connection assembly needs to be known in order to derive the ICP.
Another prior art method for measuring the ICP is by attaching a digital manometer to the inlet valve of the cuff. However, manometers are bulky and expensive devices that are not always available. The most common manometers are small battery powered devices, using one or more pressure sensors and simple circuitry to provide the required pressure. However, manometers require the connection of a conduit that reduces, when in use, the pressure within the cuff due to the additional conduit volume, therefore reducing the accuracy of the reading.
Battery or AC-powered pressure regulators are also used for measuring the ICP by means of a microcontroller, pump and valves to enable continuous control of a preset pressure. Since these devices are of a significant volume and weight, they cannot be connected directly to the ETT check valve and require additional conduit and installation procedures. Their high cost limit wide use thereof.
Another prior art device for measuring or regulating the ICP comprises an inflator bulb for manually pumping air into the cuff, e.g. the Posey Cufflator™ manufactured by the Posey Company, Arcadia, Calif. Since the cuff is in fluid communication with the inflator bulb, the ICP tends to vary while the device is attached due to the added volume of the bulb and during slow detachment of the device from the ETT, causing unintentional flow of air and a pressure inaccuracy. As a result of its considerable cost, such a prior art device is reused, leading to cross contamination and infection of intubated patients.
The medical staff is directed to routinely monitor the ICP while the patient is intubated, for example once a shift, ensuring that it continues to be within the acceptable pressure range which is indicative of proper tracheal sealing. However, due to an overload of the medical staff, particularly in an Intensive Care Unit (ICU), due to a lack of expensive ICP pressure measuring devices, or due to difficult to manipulate or inaccurate devices, this standard of care is many times not followed.
U.S. Patent Application Publication No. 2010/0179488 discloses a syringe having an internal pressure sensor comprises a syringe barrel; a piston within the barrel; a spring coupled to the piston at a first position of the spring, the spring having a second portion that is movable in response to fluid pressure within a syringe cavity; and a pressure sensor having an indicator correlated to a plurality of positions of the second portion of the spring to indicate a pressure of a fluid. The spring can be a bellows. The fluid chamber can be in fluid communication with an endotracheal tube cuff.
A considerable force has to be applied to the plunger during distal displacement in order to counteract the spring force and the sliding friction between the seal and the barrel. Another drawback of this prior art syringe is that it comprises a pressure indicator that is moveable with respect to the barrel, and therefore has to be constantly calibrated due to a changing resistance force in order to ensure accurate readings.
Pressure indicating syringes for use in other medical procedures are disclosed in EP 0589439, GB 1568283, IE 922955, WO 82/03553, WO 82/03555, WO 87/01598, WO 92/07609, WO 93/01573, U.S. Pat. Nos. 4,064,879, 4,710,172, 4,759,750, 5,163,904, 5,259,838, 5,270,685, 5,295,967, 5,449,344, 5,722,955, and US 2004/0254533.
It is an object of the present invention to provide a syringe for accurately measuring the ICP.
It is an additional object of the present invention to provide a relatively inexpensive syringe for regulating, and providing accurate readings of, the ICP while inflating or deflating the cuff surrounding a medical tube.
It is an additional object of the present invention to provide a syringe for simultaneously regulating the ICP and indicating the volume of gas added to, or removed from, a cuff during a pressure regulating operation.
It is an additional object of the present invention to provide a sufficiently inexpensive pressure regulating syringe that is disposable so as to prevent cross contamination and infection of patients.
It is an additional object of the present invention to provide a pressure regulating syringe that is operable with no more manual force that is needed by conventional syringes.
It is an additional object of the present invention to provide a pressure regulating syringe that is one time calibratable.
It is yet an additional object of the present invention to provide a pressure regulating syringe that can be connected to the check valve of a medical tube without requiring additional installation procedures.
Other objects and advantages of the invention will become apparent as the description proceeds.